Copper has attracted attention as an interconnect material as a replacement for Al and Al alloys in deep submicron integrated circuits (ICs). The major motivating factors for this are copper""s lower resistivity, superior electromigration and stress migration resistance relative to Al and its alloys. However, use of Cu metallization is not without problems. For example, Cu suffers from a lack of anisotropic etching ability, oxidation and corrosion problems, and poor adhesion to many dielectric layer. One particularly troublesome problem is the diffusion of Cu into either the Si or SiO2 layers.
In the quest to find suitable diffusion barrier layers for Cu metallizations, amorphous Tixe2x80x94Sixe2x80x94N, Moxe2x80x94Sixe2x80x94N, Wxe2x80x94Sixe2x80x94N and Taxe2x80x94Sixe2x80x94N layers have been investigated. Arnong these materials, tantalum based layers presently appear promising since they exhibit a relatively high melting temperature and are also relatively thermodynamically stable with Cu. Accordingly, significant interest exists in the use of Taxe2x80x94Sixe2x80x94N as an amorphous barrier layer for Cu metallization in semiconductors.
Tantalum silicon alloys and intermetallic compounds are used in PVD processes to provide the desired Ta/Si layers. Typically Ta/Si targets are sputtered in a reactive (e.g. N2) atmosphere to result in the formation of the desired Taxe2x80x94Sixe2x80x94N coating. Tantalum silicide alloys are commonly prepared by blending Ta and Si, usually in powder form, reacting the blend at high temperature under vacuum conditions, crushing, milling, and screening the tantalum silicide powder. These methods can be used to form known, brittle intermetallic compounds such as TaSi2 or mixtures of such intermetallic compounds with Si. Tantalum silicides having the empirical formula TaSiy wherein y less than 1 prepared by such methods are very hard alloys and cannot be milled efficiently into a powder and it is difficult to make high density targets with these materials.
Also, it is difficult to obtain full density with targets composed of Ta5Si3 and TaSi2 due to the high melting points of these crystalline compounds (e.g., 2560xc2x0 C. and 2040xc2x0 C. respectively).
For most PVD applications, a fine microstructure (or small grain size of the target material) and full density targets are required. As stated above, Ta/Si alloys with a very low content (0-10 wt %) of Si are difficult to manufacture. However, it is desirable to make targets from such alloys to inhibit silicide formation during sputtering and so that amorphous Ta/Si/N layers can be deposited via sputter coating to provide the necessary diffusion barrier layers in Cu and other metallization semiconductor circuits.
Accordingly, there is a need in the art to provide for high density TaSi sputter targets wherein the Si is present in a very low (less than or equal to about 10 wt %) amount.
Low Si content Me/Si targets (Me=refractory metal such as Ta, W, and/or Mo and combinations thereof) are provided. Preferably, the Si component is present in an amount of less than 10 wt %.
This method uses high purity Me and Si (e.g., Ta and Si) in form of powders formulated to the desirable composition. The Si can be present as an elemental powder or in the form of a metallic silicide. Preferably, this method consists of blending Me and Si (e.g., Ta and Si), loading them into a HIP can, evacuating the HIP can, and subjecting the powders to HIP conditions. Preferably, this blend includes any desirable amount of Me and Si (e.g., Ta and Silicon) and is HIPed to form a solid blank of Mexe2x80x94Si (Taxe2x80x94Si) alloy.
Sputter targets used for this process are those comprised of Ta Si0.X wherein X is from trace to about 99, preferably trace to 6, more preferably 1-6, with present data suggesting that about 3-6 is most preferred. Targets under specific investigation that have proven beneficial are:
TaSi0.1 
TaSi0.4 
TaSi0.6 
Preferably the targets are made from the powders, preferably xe2x88x9280 to xe2x88x92240 mesh, most preferably about xe2x88x92100 to xe2x88x92200 mesh. In some instances it will be necessary to ball mill the powder. The particles are blended together and then HIPed so as to obtain preferably greater than about 98% theoretical density, more preferably greater than about 99% theoretical density, most preferably about 99.5% theoretical density. HIPing is generally conducted at about 20,000-40,000 psi at temperatures of about 1100-1350xc2x0 C. for about 1-4 hours.
After HIPing, the targets can be shaped into the final needed target shape such as rectangular flat panels, circular targets, conical targets etc. via light machining or the like. The targets have shown promise in reactive sputtering systems and applications wherein N2 is the reactive gas.
In addition to Ta/Si targets, other transition metals may be substituted for the Ta. A listing of such other metals includes W, Mo, and Ti.
Accordingly the following targets may be made via the inventive methods
MeSi0.X
wherein Me is a transition metal, preferably taken from the groups IVb, Vb, and VIb of the Periodic Table of Elements (CAS Version), more preferably Ta, W, Mo, Ti, most preferably Ta. X in the above formula may be from about tracexe2x80x9499, tracexe2x80x946, preferably 1-6 and most preferably 3-6.
The prior art mentions Ta5Si3 targets and their use to sputter improved diffusion barrier layers. However, it is thought that this composition comprises intermetallic compound Ta5Si3. In contrast, targets in accordance with the invention are multi-phase.
The targets of the invention are used in conventional sputter coating equipment, preferably with N2 used as the reactive gas, thereby sputter coating the desired substrate with a layer of amorphous Mexe2x80x94Sixe2x80x94N.